1. Field of the Invention and Related Art Statement:
This invention relates to an endoscope still photographing apparatus provided with a control means setting the illuminating light amount to be of the optimum value before starting an exposure.
Recently, an endoscope has come to be extensively used in the medical field and industrial field.
Now, in order to make a detailed diagnosis with an endoscope or to know the variation with the lapse of time of an affected part, a photographing is often made. As disclosed, for example, in the publication of a Japanese Patent Application Laid Open No. 13236/1986, the assignee has suggested an apparatus wherein, in the case of photographing at a short distance, in order to make a controllable shutter speed, how much the diaphragm is to be diaphragmed at the time of photographing from the present EE level and diaphragm position is calculated and, in case the object at the short distance is very bright, the calculated diaphragm is diaphragmed to photograph the object so that the shutter speed may be within a controllable range to prevent an over exposure.
This photographing sequence shall be explained. The camera is to be fitted to the eyepiece part of the scope. If the diaphragm and shutter are incorporated on the camera side, the size will become so large as to reduce the operatability. Therefore, the diaphragm and shutter are incorporated on the light source side and are controlled with respective signals transmitted to the light source side from the camera side. In order to omit one of the signal lines, the diaphragm controlling signal and shutter controlling signal are transmitted through one line. FIG. 1 shows respective timing charts of the control signal (EE signal), shutter and diaphragm.
A: At the time of the automatic light adjustment, the diaphragm will be controlled by the signal (EE signal) obtained by converting the light from the image guide to an electric signal. The shutter remains open.
B: When a release signal is made within the camera, the shutter will tend to close and the diaphragm will tend to open.
C: The diaphragm opens and the shutter closes.
D: The shutter opens with an integration starting signal and closes with an integration ending signal. The diaphragm remains open.
E: When the mirror on the camera side closes and no light comes into the film, the shutter will open.
F: The state of A returns.
In the case of exposing at a short distance, the diaphragm will be diaphragmed for the period of D so as not to make an over exposure.
Such photographing sequence as in the above has been so far used.
However, in fact, if the light amount at that time is judged from the position of the diaphragm, it will be found that, in case the precision becomes low particularly in the diaphragmed direction and thereby the diaphragm is diaphragmed too much, the exposure amount will be well kept at the regulated value but the shutter speed will become so long that the exposure amount will be likely to collapse. In order to improve it, as explained in a Japanese Patent Application No. 195901/1982, the assignee has provided a hard means of controlling the diaphragm in the opening direction after the lapse of a fixed period after the starting of the exposure. Anyhow, with these methods, it is difficult to make the optimum diaphragmed amount and a large burden has been applied to the CPU forming the control means.
By the way, an exposure controlling means is disclosed in U.S. Pat. No. 4,353,630. However, even if this prior art example is applied to the endoscope still phototographing apparatus, the above mentioned problems will not able to be solved.